Health Library

Colorectal Cancer Screening

Colorectal cancer (cancer in the colon or rectum) is a leading cause of cancer deaths in the United States. But it doesn’t have to be. When this cancer is found and removed early, the chances of a full recovery are very good. Because colorectal cancer rarely causes symptoms in its early stages, screening for the disease is important. It’s even more crucial if you have risk factors for the disease. Learn more about colorectal cancer and its risk factors. Then talk to your doctor about being screened. You could be saving your own life.

Risk Factors for Colorectal Cancer

Your risk of having colorectal cancer increases if you:

Are 50 years of age or older

Have a family history or personal history of colorectal cancer or polyps

Have a personal history of type 2 diabetes, Crohn’s disease, or ulcerative colitis

Have an inherited genetic syndrome like Lynch syndrome (also known as HNPCC) or familial adenomatous polyposis

Are very overweight

Smoke

Drink a lot of alcohol

Eat a lot of red or processed meat

The Colon and Rectum

Waste from food you eat enters the colon from the small intestine. As it travels through the colon, the waste (stool) loses water and becomes more solid. Intestinal muscles push it toward the sigmoid — the last section of the colon. Stool then moves into the rectum, where it’s stored until it’s ready to leave the body during a bowel movement.

How Cancer Develops

Polyps are growths that form on the inner lining of the colon or rectum. Most are benign, which means they aren’t cancerous. But over time, some polyps can become malignant (cancerous). This occurs when cells in these polyps begin growing abnormally. In time, malignant cells invade more and more of the colon and rectum. The cancer may also spread to nearby organs or lymph nodes or to other parts of the body. Finding and removing polyps can help prevent cancer from ever forming.

Your Screening

Screening means looking for a medical problem before you have symptoms. During screening for colorectal cancer, your doctor will ask about your medical history, examine you, and do one or more tests.

History and Exam

Medical history. Your doctor will ask about your medical history. Mention if a family member has had colon cancer or polyps. Also mention any health problems you have had in the past.

Digital rectal exam (DRE). During a DRE, the doctor inserts a lubricated gloved finger into the rectum. The test is painless and takes less than a minute. Doctors agree that this test alone is not enough to screen for colorectal cancer.

Screening Test Options

Fecal occult blood test or fecal immunochemical test

These tests check for occult blood in stool (blood you can’t see). Hidden blood may be a sign of colon polyps or cancer. A small sample of stool is tested for blood in a laboratory. Most often, you collect this sample at home using a kit your doctor gives you. Follow the instructions carefully for using this kit. You might need to avoid certain foods and medications before the test, as directed.

Barium enema with contrast

This test uses X-rays to provide images of the entire colon and rectum. The day before this test, you will need to do a bowel prep to clean out the colon and rectum. A bowel prep is a liquid diet plus strong laxatives or enemas. You will be awake for the test, but you may be given medication to help you relax. At the start of the test, a radiologist (a doctor who specializes in imaging tests) places a soft tube into the rectum. The tube is used to fill the colon with a contrast liquid (barium) and air. This can be uncomfortable for some people. The liquid helps the colon show up clearly on the X-rays. Because the test uses X-rays, it exposes you to a small amount of radiation.

Virtual colonoscopy

This exam is also called a CT colonography. It uses a series of X-ray photographs to create a 3-D view of the colon and rectum. The day before the test, you will need to do a bowel prep to clean out your colon. Your health care provider will give you instructions on how to do this. During the procedure, you will lie on a table that is part of a special X-ray machine called a CT machine. A small tube will be placed into your rectum to fill the colon and rectum with air. This can be uncomfortable for some people. Then, the table will move into the machine and photos will be taken of your colon and rectum. A computer will combine these photos to create a 3-D picture. Because the test uses X-rays, it exposes you to a small amount of radiation.

Scope exams

Colonoscopy. This is the best test doctors have for finding and removing colorectal polyps. The day before the test, you will do a bowel prep. This is a liquid diet plus a strong laxative solution or an enema. The bowel prep will cleanse your colon. You will be given instructions for this. Just before the test, you are given a medication to make you sleepy. Then, a long, flexible, lighted tube called a colonoscope is gently inserted into the rectum and guided through the entire colon. Images of the colon are viewed on a video screen. Any polyps that are found are removed and sent to a lab for testing. If a polyp can’t be removed, a sample of tissue is taken and the polyp might be removed later during surgery.

Sigmoidoscopy. This test is similar to colonoscopy, but focuses only on the sigmoid colon and rectum. As with colonoscopy, bowel prep must be done the day before this test. It might not need to be as complete as the bowel prep for a colonoscopy. You are awake during the procedure, but you may be given medication to help you relax. During the test, the doctor guides a thin, flexible, lighted tube called a sigmoidoscope through your rectum and lower colon. The images are displayed on a video screen. Polyps are removed, if possible, and sent to a lab for testing.

Colonoscopy is the only screening test that lets your doctor see the entire colon and rectum. This test also lets your doctor remove any pieces of tissue that need to be looked at by a lab. If something suspicious is found using any of these other tests, you will likely need a colonoscopy.

When to Call Your Doctor After a Test

Call your doctor if you have any of the following after any screening test: